The present invention relates generally to satellite communication systems, and more particularly to an apparatus and method for transmitting and receiving signals from multiple orbit positions that provide service to diverse geographical areas using a single identical reflector.
Satellite systems are widely used for various communication services in various locations around the world. Each satellite system is assigned a particular orbital slot based on the specific service, geographical coverage area, power requirements, and other related system requirements and criteria. Satellite systems include multiple antennas each of which having a reflector surface that is designed to transmit and receive communication signals from the assigned orbital slot and for an assigned coverage area. A coverage area may contain multiple regions of coverage. Each region of coverage has different signal requirements including directivity and link availability. Link availability incorporates various signal requirements including gain, rain fade margin, slant range attenuation, cross-polarization interference and discrimination, and clear sky margin requirements for different regions of coverage. Each reflector has a surface that is shaped for maximizing signal transmission from each of the assigned orbital slot to meet or exceed the link availability requirements for all the regions of the assigned coverage area.
Satellite system capability requirements are continuously increasing to accommodate more and more services. In doing so, it has become desirable for a satellite system to have the capability of being used in multiple orbital slots and to provide services for multiple coverage areas. Several factors are considered in developing such a satellite system. One factor is that the satellite system should be designed to provide coverage to the same coverage area from different orbital slots while meeting multiple signal requirements. Transmission beams need to be weighted differently to compensate for the varying rain-fade corresponding to different rain zones within the coverage area. Furthermore, different gains need to be provided for the same location within the coverage area but for the satellite located at different orbit slots in order to compensate for the different rain attentions due to different slant ranges. Slant range refers to the distance the satellite signals must travel through the earth""s atmosphere in order to reach the earth based station that it is in communication with. For example, a satellite system located over the west portion of the United States directs signals towards the east portion of the United States will have a shallow elevation angle and require a different gain for its transmitted signals than would a satellite system positioned directly over the east portion of the United States. Moreover, factors such as high level interference from cross-polarized spot beams on a satellite shaped beam, adjacent satellite and adjacent channel interference, self cross-polarization interference, low ground terminal cross-polarization discrimination, and satisfaction of a minimum clear-sky link margin requirements also need to be considered in the design.
In order to achieve all the above-mentioned factors, satellite systems having antennas with multiple reflectors are traditionally required where each reflector is shaped for a specific orbital slot. This limits the number of apertures that can be accommodated on the same satellite system for spot beams and other satellite payloads.
Current satellite systems are also designed to prevent signal interference in the assigned orbital slots and the assigned coverage area, in which case they are not interference limited for multiple service areas.
Therefore, it would be desirable to provide an improved satellite system that uses a single antenna reflector that has the ability to operate in multiple orbits and for multiple coverage areas that are interference limited.
The foregoing and other advantages are provided by an apparatus and method for transmitting communication signals. A synthesized reflector surface for directing communication signals in a communication system that operates in a plurality of orbital slots and to a plurality of regions within a first coverage area is provided. The synthesized reflector surface includes a plurality of contiguous profile surfaces that form the reflector surface. Each of the plurality of contiguous profile surfaces alters the phase of the communication signals to provide a first gain for a first satellite orbit location and a second gain for a second satellite orbit location. The plurality of contiguous profile surfaces directs the signals from the first satellite orbit location in a first orientation to the first coverage area or from the second satellite orbit location in a second orientation to the first coverage area.
A method is also provided for synthesizing the reflector surface including determining a plurality of orbital slots. Plurality of coverage area(s) are also determined for the plurality of orbital slots. The reflector surface is shaped in response to the plurality of orbital slots and the plurality of coverage areas such that the reflector surface transmits communication signals to a first coverage area from plurality of said plurality of orbital slots. Directivity values of communication signals for the plurality of orbital slots and the coverage areas are calculated. Link availability for the plurality of orbital slots and the coverage areas in response to the computed directivity values are determined. The system determines whether the directivity values and the link availability have been satisfied in the shaped reflector surface.
A satellite system and a method of configuring the satellite system are also provided utilizing the synthesized reflector surface.
One of several advantages of the present invention is that it is flexible in that it may be used in multiple orbits and provides coverage for multiple geographical coverage areas. The flexibility of the present invention allows it to be used for various communication services.
Another advantage of the present invention is that in accounting for different aspects of link availability for multiple regions of coverage, it is capable of operating in an interference-limited environment, which further provides increased flexibility as to operate in multiple orbital slots.
Furthermore, the present invention provides different gains for different regions of coverage area in order to compensate for the difference in the rain attenuation values over the intended coverage on earth.
The present invention itself, together with further objects and attendant advantages, will be best understood by reference to the following detailed description, taken in conjunction with the accompanying figures.